Rhipidomella (Oehlert 1890) is another common brachiopod from the Haragan Fm. as well as from the Silurian thru the Carboniferous. The book "Stratigraphy and Paleontology of the Hunton Group in the Arbuckle Mountain Region" 1958 Thomas Amsden and Arthur Boucot, Oklahoma Geological Survey, Bulletin 78; does not specify any particular species for these shells. Apparently at the time there was some discussion about how to classify the shells found in the Haragan and if they deserved a new genus based on thin sections of how the crenulations of the shells interlocked at the lip. Thanks to a fellow Fossil Forum member, I can now ID this as Rhipdomelloides oblata
This specimen came from an old estate collection of fossils that were collected in the 1960's to 1970's from the Haragan Formation at White Mound, OK. The Haragan formation is thought to range from the upper Silurain, 418mya, to the lower Devonian, 411mya ( Pridoli to Lochkovian). This would correspond to the Birdsong shale of Tennessee and the Helderberg Fauna of New York, Pennsylvania and Maryland.